1. Field of the Invention
The present invention pertains to stackable risers. More particularly, the present invention pertains to a system and method of connecting a series of risers in a way that provides improved vertical support, minimizes the effect of frost heaving and other forces due to vertical ground movement, and resists rotational forces resulting from lateral ground movement.
2. Background of the Invention
Meters, splices, junction boxes, and other components of buried utility systems are often located inside hand-holes or manholes to enable easy access by utility workers from aboveground. Often, utility systems provide such access facilities at key points, such as a major bend in an underground cable/conduit run or location of water or gas meters and other equipment subject to frequent servicing or inspection. Such access facilities have been constructed using preformed or poured concrete side retaining walls. Concrete can be expensive, particularly where the application requires a non-standard size or length, in which case setting forms and pouring concrete adds time and expense. Also, over time, the concrete can crack due to forces caused, for example, by freezing and thawing or by heavy vehicles being driven over the top of the manhole. Tiled sidewalls and concrete block are examples of other labor intensive alternatives.
Injection molded, plastic, stackable risers made of high density polyethylene and other rigid, light weight polymeric material are known in the art and provide a less expensive, standardized alternative that lends itself to rapid on site customization. Risers can be manufactured in various heights and diameters and a series of identically sized risers can be stacked to achieve a desired depth.
Depending on the soil characteristics and overhead traffic, the vertical, horizontal, and rotational forces placed upon these risers can be considerable. A major shortcoming of plastic risers lies in their tendency to deform or break when subjected to such forces. The use of vertical and horizontal strengthening ribs to alleviate this tendency is common. When placed along the exterior of the sidewall, however, these reinforcing ribs themselves often are subjected to the same vertical and horizontal forces they are intended to protect against.
U.S. Pat. No. 5,852,901 for a xe2x80x9cStackable Riser for On-Site Waste and Drainage Systems,xe2x80x9d issued to Meyers illustrates one prior art design of a plastic riser for forming a depth-adjustable, grade-level access for underground components. The Meyers riser forms a rigid structure intended to support heavy loads applied to the grade level access lid. Identical risers reinforced along portions of both the inner and outer walls are stacked one on top of the other utilizing a single tongue and groove connection. A horizontal rib extending outward along the circumference of the external surface of the side wall of each cylindrical riser and a plurality of vertical ribs, also on the external surface of the riser, individually anchor each riser in the ground. A plurality of risers can be stacked to form a vertical, air-tight, liquid-tight, and gas-tight riser and lid system.
The shifting of the ground surrounding the riser stack disclosed in the Meyers patent can twist and move the stacked risers, knocking them out of alignment. Eventually, the shifting can lead to rupture of the stacked risers"" sidewall. The presence of external horizontal and vertical reinforcing ribs extending along the wall of each riser, while strengthening the riser sidewalls, also exacerbates this problem because shifting soil applies force against each exposed rib. The configuration of the tongue and groove arrangement of the risers disclosed in the Meyers patent also precludes the placement of supporting ribs along the full vertical length of the interior riser wall, which lessens the sidewall""s resistance to forces exerted by the shifting of the soil abutting the sidewalls and external ribs.
The stackable riser of the present invention addresses these shortcomings. In the preferred embodiment, the stackable riser of the present invention has a hollow, cylindrical configuration, although configurations other than cylindrical may be used. The sidewall of the riser includes a channel end and a tapered end. In the preferred embodiment, the riser has a nearly smooth exterior surface from which projects outwardly a detachable anchor tab that may run along substantially the full circumference of the riser. The channel end of the riser sidewall includes two adjoining channels which are defined by interior, middle, and exterior walls that project concentrically with, or (in the case of risers having, for example, a square or rectangular cross-section) parallel to, the sidewall. The opposite, or tapered, end of the riser sidewall terminates in a portion tapered to a narrower thickness at the end. A plurality of vertical reinforcing ribs are spaced around the interior surface of the cylindrical sidewall of the riser. Because in the preferred embodiment the ribs extend from near the channel end to the distal end of the tapered end of the riser sidewall, they strengthen the sidewall in the area of the joint between each pair of stacked risers. In the preferred embodiment, the interior surface of the sidewall also includes at least one boss extending vertically from near the channel end to the distal end of the tapered end of the riser. Each boss is adapted to receive a screw, or other fastener, for securing another riser stacked on top of the first riser, or a cover at ground level.
The tapered end of the riser sidewall is configured to mate with the two concentric channels of either another riser or a cover. The radially outer channel is shallower than the inner channel in the preferred embodiment and accepts the tapered end of the sidewall of another riser on which it is placed. The radially inner channel is wider than the outer channel, and accepts the interior vertical support ribs and bosses of a riser on which it rests. An O-ring placed in the outer channel can be used to effect a water-tight and gas-tight seal between two stacked riser sections (or between a riser and a cover). Sealant can be applied to the area where the tapered end of a first riser contacts the outer channel of another riser (or a cover) stacked on top of the first riser to further ensure a water-tight, gas-tight seal between adjacent risers (or between a riser and a cover) beyond that provided by the dual channel design of the present invention.
In the preferred embodiment, a detachable anchor tab on the exterior surface of the riser sidewall serves to anchor the lower-most riser in concrete, for example, a cast-in-place concrete distribution box. The concrete is poured around the riser and its anchor tab, thereby anchoring the bottom riser after the concrete hardens. Another identical riser may be placed on top of the bottom riser, with the tapered end of the bottom riser mating with the channel end of the riser placed on top of the bottom riser. The anchor tab on each of the risers stacked above the bottom riser (i.e., above the riser anchored in the concrete box) in a given stack can be detached by tearing it away from the exterior of the sidewall. In the preferred embodiment, the anchor tab includes a handle for this purpose. Tearing away the anchor tabs on the risers that are not anchored in concrete gives the stack of risers a nearly smooth exterior surface, thereby minimizing the forces exerted on the stack of risers by movement of the soil in contact with the riser stack.
In alternative embodiments of the present invention, the risers may have a square, rectangular, elliptical or other cross-sectional configuration.
It is an object of the present invention to provide an improved connection configuration that resists rotational forces exerted on one or more risers in an interconnected system.
It is another object of the present invention to provide improved reinforcement of the sidewalls of risers stacked one on top of the other.
It is still another object of the present invention to provide a detachable anchor on the exterior surface of a riser, the anchor being used when the riser is to be anchored in concrete, and removed when the riser is to be in contact with soil.
It is a further object of the present invention to provide a riser adapted for being anchored in concrete, while at the same time minimizing the susceptibility of a stack of risers to forces caused by the ground next to the stack shifting.
Other features, objects and advantages of the invention will become apparent from the following description and drawings in which the details of the invention are fully and completely disclosed as part of this specification.